Spatial Characteristics and Driving Forces of Biomass of Pinus massoniana Forest in a Typical Red Soil Region of Southern China

Based on the forest resource inventory of Changting County, the aboveground biomass of Pinus massoniana was estimated, and its spatial characteristics were analyzed by global Moran's I index and the hot spot analysis(Getis–Ord G_i^* ). The geographical detectors were used to explore its influencing factors, and the structural equation model was constructed to clarify its driving mechanism. The results showed that the aboveground biomass of P. massoniana in the study area was 53.563 t/hm², with obvious spatial distribution differences. The spatial characteristics were shown as high-value clustering in the west and north of the study area and low-value clustering in the center and south. The results of geographic detectors showed that canopy density, elevation, stand age, mean annual temperature, precipitation, soil organic matter and soil total nitrogen content were significant influencing factors for biomass spatial differentiation of P. massoniana in the study area, and the explanatory power was enhanced by two-factor interaction. The path analysis of structural equation model showed that the main factors driving the path were canopy density, stand age, elevation and average annual precipitation. Canopy density exerted direct effect on biomass, while elevation indirectly affected stand biomass by influencing the precipitation and temperature. Stand age and mean annual precipitation had both direct and indirect effects on biomass, stand age had an indirect effect by affecting canopy density, and mean annual precipitation as well by affecting soil total nitrogen. In summary, the aboveground biomass of P. massoniana in Changting County shows significant spatial clustering distribution characteristics. The central and southern regions of the study area are the key areas for further improvement of P. massoniana stand quality and ecological management. In the future, the management of P. massoniana in Changting County can be focused on enhancing the stand quality by optimizing the stand structure, increasing the canopy density and improving soil nutrients.